<!DOCTYPE html>
<html lang="zh-CN">
    <head>
        <meta charset="UTF-8" />
        <title>05_颜色属性-为什么要有px</title>
        <style>
            #d1 {
                /* cm mm*/
                width: 1cm;
                height: 1cm;
                background-color: aquamarine;
            }

            #d2 {
                width: 1mm;
                height: 1mm;
                background-color: red; 
            }

            #d3 {
                width: 1mm;
                height: 1mm;
                background-color: purple; 
            }

            #d4 {
                width: 100px;
                height: 100px;
                background-color: yellow; 
            }

        </style>
    </head>
    <body>
        <div id="d1"></div>
        <div id="d2"></div>
        <div id="d3"></div>
        <hr>
        <div id="d4"></div>
    </body>
</html>